The Pentagon is defending a deadly air strike on the Pakistan-Afghan border that killed 11 Pakistani soldiers and drew strong protests from the government in Islamabad. VOA correspondent Meredith Buel has details from Washington.

Pentagon Press Secretary Geoff Morrell says the strike by three aircraft just inside the Pakistani border with Afghanistan is justifiable.

"In these early hours after this strike every indication we have is that this was a legitimate strike against forces that had attacked members of the coalition," he said.

Reports say about a dozen bombs were dropped into Pakistan. Morrell says the strike came after militants attacked coalition forces near a checkpoint 200 meters inside Afghanistan's eastern Kunar province.

"Our forces came under attack, came under fire from forces that had come over from the Pakistani side into Afghan territory and then retreated into Pakistani territory and continued to fire upon our forces even though we did not pursue them into Pakistan," he said.

The attack brought immediate outrage from Pakistan, where an army spokesman called it an unprovoked and cowardly act.

The government in Islamabad lodged a diplomatic protest against the United States and U.S. Ambassador Anne Patterson was summoned to the Foreign Ministry.

Morrell says the Pentagon is investigating the incident.

"We are aware of some of the concerns that have been expressed by the Pakistani Army and other elements of the Pakistan government. I can tell you that we are working with the Pakistani government to try to get to the bottom of this incident so that they have a better understanding of it. So that we have a better understanding of it," he said.

The Pentagon spokesman declined to confirm that Pakistani soldiers were killed in the attack.

However at the U.S. State Department acting spokesman Gonzalo Gallegos released a statement.

"This is a regrettable incident. We are sad to see the loss of life among the Pakistani military, who are partners in fighting terror. This is a reminder that better cross-border communications between forces is vital," he said.

While details of the incident remain unclear, the Pentagon says the attack was coordinated with Pakistani forces.

A statement released by U.S. military officials in Afghanistan says an unmanned aircraft was used to maintain positive identification of the enemy firing at coalition troops.

The Pakistani army says the bombs hit a post of the paramilitary Frontier Corps.

The air strike has upset the already fragile relations between Washington and Islamabad over how to stem violence and fight terrorists in the region that is inside Pakistan but outside the law.

"We, as I have said before, have a shared, vital interest in making sure that militants, terrorists, insurgents, others operating in these Federally Administered Tribal Areas do not have the means to mount attacks against the Pakistani government or any other government for that matter," he said.

The incident has inflamed anti-U.S. sentiment inside Pakistan, where a new government is trying to reach out to tribal leaders in the border region to negotiate a peace deal.

U.S. officials have expressed skepticism about the plan, and there have been repeated questions about Pakistan's commitment and ability to battle terrorists known to be hiding in the mountainous terrain.